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Antarctic land ice stores the majority of Earth’s freshwater and carries substantial uncertainties regarding its future contribution to global sea level rise. While ocean processes associated with basal melting currently dominate ice loss, atmospheric forcing could have an increasing future impact, especially with intensified extreme weather events. For instance, atmospheric rivers, which are key drivers of long-distance moisture transport, introduce significant uncertainties to Antarctica’s ice mass balance, as they are capable of causing both intense snowfall and surface melting. They also impact ocean stratification and mixed-layer depth through freshwater input, ultimately affecting air-sea exchange. Associated interactions among components of the Earth system—atmosphere, ocean, and glacier—are not fully captured by global climate models and observations. This paper assesses Antarctica’s future, highlighting uncertainties stemming from limited understanding of atmospheric and oceanic forcings such as atmospheric rivers, and their consequences for projecting sea-level rise-related hazards. 

Abstract Recent decades have seen record-high temperatures on the Antarctic Peninsula (AP) due to combined atmospheric rivers (ARs) and föhn warming. While ARs frequently enhance föhn, not all events cause surface warming over the entire Larsen C Ice Shelf (LCIS). Using high-resolution Polar WRF simulations, we examine the relationship between ARs and föhn over the AP during austral summers and identify four distinct AR shapes associated with föhn-induced surface warming over the LCIS: zonal-perpendicular, zonal-like, convex, and concave. Zonal-like ARs associated with coupled low-high-pressure systems and convex ARs linked to blocking highs produce strong föhn warming across the entire LCIS, primarily affecting its northern and southern sectors, respectively. In contrast, zonal-perpendicular and concave ARs generate moderate-to-weak warming, owing to either weaker AR intensity or AR curvature. Although downward shortwave radiation dominates surface warming, enhanced moisture suppresses its increase from föhn-induced cloud clearance while enhancing downward longwave radiation near mountain gaps. Sensible heat flux also contributes substantially along the mountain foothills. As ARs intensify under climate change, their interaction with föhn over the AP can critically influence the future stability of coastal ice shelves. 

Abstract The record‐breaking Arctic cyclone of January 2022 caused an unprecedented sea ice loss in the Barents Sea near Svalbard, which was severely underestimated by both the ECMWF operational forecast and the CESM1 global climate model. To investigate this discrepancy and further explore the mechanisms that led to sea ice loss, we utilize a regional ocean–sea ice MITgcm model forced with ERA5 atmospheric reanalysis, validated against satellite‐derived ice concentrations and thickness, and Argo observations. We tested model sensitivity to initial conditions by choosing two different ocean reconstructions and tested sensitivity to the air‐sea‐ice drag coefficient. The model shows that cyclone‐driven winds induced strong upper‐ocean mixing of cold, fresh polar waters with subsurface warm, salty Atlantic Water, bringing heat to the surface to rapidly melt thin seasonal ice north of Svalbard. This process was evident in Argo float profile changes but not in the operational forecast and global climate model. In contrast, wind‐driven mechanical divergence dominated sea ice loss south of Svalbard, where the direction of sea ice retreat followed the direction of the prevailing winds. Increasing the air‐ice drag coefficient substantially improved the agreement between our modeled and observed ice area evolution. The balance between thermodynamic and mechanical effects on the sea ice loss was highly sensitive to drag parameterization. Our results highlight the need to improve the representation of upper ocean stratification, vertical mixing, and air‐sea‐ice momentum fluxes to reproduce cyclone‐triggered rapid sea ice loss events in the Arctic in winter. 

Abstract Global reanalyzes are widely used for investigations of Antarctic climate variability and change. The European Centre for Medium‐Range Weather Forecasts 5th generation reanalysis (ERA5) is well regarded and spans 1940 to today. We investigate whether ERA5 reliably represents the 2‐m air temperature trends across the 1940–2022 (83 years) period at seasonal and annual time scales. We compare ERA5 temperatures with an observation‐based temperature reconstruction for Antarctica (RECON) that has monthly resolution for 1958–2022, the period of reliable observational availability. Results for individual stations are also examined. ERA5 anomalously warms Antarctica in relation RECON especially for the period prior to 1979 when satellite observations over the Southern Ocean were sparse. Trend hotspots that are shown to be artifacts are found at three locations and are present until today. The results demonstrate that ERA5 temperature trends can be questionable even today, but variability is well captured after 1979. 

Abstract. Atmospheric rivers (ARs) are the primary mechanism for transporting water vapor from low latitudes to polar regions, playing a significant role in extreme weather in both the Arctic and Antarctica. With the rapidly growing interest in polar ARs during the past decade, it is imperative to establish an objective framework quantifying the strength and impact of these ARs for both scientific research and practical applications. The AR scale introduced by Ralph et al. (2019) ranks ARs based on the duration of AR conditions and the intensity of integrated water vapor transport (IVT). However, the thresholds of IVT used to rank ARs are selected based on the IVT climatology at middle latitudes. These thresholds are insufficient for polar regions due to the substantially lower temperature and moisture content. In this study, we analyze the IVT climatology in polar regions, focusing on the coasts of Antarctica and Greenland. Then we introduce an extended version of the AR scale tuned to polar regions by adding lower IVT thresholds of 100, 150, and 200 kg m−1 s−1 to the standard AR scale, which starts at 250 kg m−1 s−1. The polar AR scale is utilized to examine AR frequency, seasonality, trends, and associated precipitation and surface melt over Antarctica and Greenland. Our results show that the polar AR scale better characterizes the strength and impacts of ARs in the Antarctic and Arctic regions than the original AR scale and has the potential to enhance communication across observational, research, and forecasting communities in polar regions. 

Radiosonde observations over Antarctica and the surrounding oceans were enhanced during the Year of Polar Prediction in the Southern Hemisphere (YOPP‐SH) summer Special Observing Period (SOP). Observing System Experiments (OSEs) were conducted in a continuous cycling framework using the Weather Research and Forecasting (WRF) Model and its data assimilation system. Routinely available observations were assimilated in the CTL (control) experiment, and special radiosonde observations from the YOPP‐SH SOP were additionally assimilated in the YOPP experiment. The results were compared to investigate the effects of additional radiosonde observations on analyses and forecasts over and around Antarctica. Verifications against ERA5 re‐analysis, radiosonde observations, and Automatic Weather Station (AWS) observations show overall positive effects of additional radiosonde observations. These positive effects are most noticeable in temperature at lower levels at earlier forecast lead times; afterward, wind forecast improvements at upper levels are the most noticeable. Although routine and special radiosonde observations are concentrated over the eastern and coastal regions of Antarctica (compared to the western and inland regions), the effects of the extra data spread in longitudinal and latitudinal directions; therefore, the effects on the forecasts are not limited to only the areas near the radiosonde observations. A case study reveals how cyclone forecasts are improved through the assimilation of the additional YOPP‐SH SOP radiosonde observations. This study provides insights into future observation strategies in Antarctica, such as horizontal/vertical observation locations, observation variables, and so forth to maximize effects of new observations on forecasts over Antarctica.